The asphalts now generally commercially produced encounter problems due to the viscoelastic behavior and low temperature performance along with resistance to flow at high temperatures. These characteristic defects are well known to those skilled in the art. It has been the practice, heretofore, to treat asphalt in order to attempt to obtain a more desirable material. One conventional treatment for this purpose involves blending air blown and other asphalts with a small amount of an olefin polymer and other resins, as is exemplified in U.S. Pat. No. 3,329,636 which does not mention or suggest blowing a polymer/asphalt blend.
Other methods to produce asphalt materials include, for example, blending asphalt and polystyrene-polybutadine-polystyrene (SBS) or polystyrene-polyisoprene-polystyrene (SIS) polymers (also sometimes referred to as ABA-type polymers). Representative patents showing such blends include U.S. Pat. Nos. 4,530,652; 4,824,880; 4,835,199; 4,923,913; 5,036,119 and 4,559,267. These references do not show the concept of blowing blends of such types of polymers in asphalt. Further, these blends would require high shear mixing equipment in order to form an asphalt material. In the past this type of equipment has not been used in asphalt processing plants.
Further, U.S. Pat. No. 4,585,816 which discusses the problems associated with the presence of air during the blending operation of asphalt with block copolymers also fails to teach blowing blends of polymer and asphalt.
It is also known to react ABA (or SBS) type polymers and asphalt blends using free radical generators such as for example, peroxide compounds as discussed in for example, U.S. Pat. Nos. 4,503,176 and 4,956,500. However, these do not disclose air blowing a blend of asphalt and polymer.
Further, it has been known that a blend of asphalt and an ethylene-vinyl-acetate copolymer can be air blown, as disclosed in U.S. Pat. Nos. 4,454,269 and 4,425,454. In particular, the '269 reference discusses that in simple blending of EVA with already air blown, high softening point industrial asphalt that the blend was incompatible. While the '269 patent uses a particular asphalt/EVA blend and air blowing method, comparative testing conducted by the inventors herein showed that the EVA-based products produced incompatible materials. Further, these references do not teach or suggest the use of styrene-based block copolymers.
Thus, there is a need to further develop specific asphalt polymer systems which are superior to the asphalt-EVA blown blends and are superior to materials formed from typical polymer blends with asphalt. Further, mere blends of SBS and SIS polymers with previously air blown asphalts are extremely incompatible to the point of not being useful materials.
It is therefore an object of the present invention to provide a process for preparing compositions of SBS and SIS polymers blended and reacted into asphalt wherein the product of the process has excellent tensile and enlongation properties and compatibility and also has acceptable storage stability.
In another aspect, it is an object of the present invention to provide an elastomeric-asphalt composition which is the product of this process.